GPC3 and hepatocellular carcinoma: <b>Methods:</b> This multicenter, open-label, nonrandomized first-in-human phase 1 dose escalation and expansion study aims to evaluate the safety, tolerability, pharmacokinetics, and antitumor activity of <sup>225</sup>Ac-GPC3 ACC, with or without preinjection of the nonradioactive GPC3 ACC, in participants with advanced HCC.